It's the star's first tour in seven years, after taking time out to start a family with her partner, Spanish footballer Gerard Pique.
Footage from the opening night in Hamburg showed the 41-year-old looking overwhelmed, clasping her hands to her chest as she acknowledged her long journey back to health.
"Last year was one of the most difficult times of my entire life," she tells the BBC from Amsterdam. "Being back on stage has been so emotional."
